Broadband Impedance Matching of Antenna Radiators

In the design of any antenna radiator, single or multi-element, a significant amount of time and resources is spent on impedance matching. There are broadly two approaches to impedance matching; the first is the distributed impedance matching approach which leads to modifying the antenna geometry itself by identifying appropriate degrees of freedom within the structure. The second option is the lumped element approach to impedance matching. In this approach instead of modifying the antenna geometry a passive network attempts to equalize the impedance mismatch between the source and the antenna load. This thesis introduces a new technique of impedance matching using lumped circuits (passive, lossless) for electrically small (short) non-resonant dipole/monopole antennas. A closed form upper-bound on the achievable transducer gain (and therefore the reflection coefficient) is derived starting with the Bode-Fano criterion. A 5 element equalizer is proposed which can equalize all dipole/monopole like antennas. Simulation and experimental results confirm our hypothesis. The second contribution of this thesis is in the design of broadband, small size, modular arrays (2, 4, 8 or 16 elements) using the distributed approach to impedance matching. The design of arrays comprising a small number of elements cannot follow the infinite array design paradigm. Instead, the central idea is to find a single optimized radiator (unit cell) which if used to build the 2x1, 4x1, 2x2 arrays, etc. (up to a 4x4 array) will provide at least the 2:1 bandwidth with a VSWR of 2:1 and stable directive gain (not greater than 3 dB variation) in each configuration. Simulation and experimental results for a solution to the 2x1, 4x1 and 2x2 array configurations is presented

Low-Profile Antennas for Aircraft Communication Systems

RÉSUMÉ Dans les aéronefs, les antennes sont utilisées pour les communications ainsi que pour différents systèmes de navigation allant de 30 MHz à 4 GHz et plus. Le positionnement des antennes sur l'aéronef est crucial pour les systèmes avioniques. Les antennes de type « lame » (blade antennas) sont généralement utilisées dans l’aéronef pour divers systèmes de communication. L’antenne lame est essentiellement un monopole qui fait généralement autour d’un quart à un huitième de longueur d’onde et est encapsulée dans un radôme. À basse fréquence, la taille de la lame devient suffisamment grande pour introduire du bruit, augmenter la traînée aérodynamique de l'antenne et causer des dommages suite à une collision avec des équipements au sol lors de l’entretien et le service de l'aéronef. Par conséquent, et afin d’améliorer l'aérodynamisme des avions commerciaux efficaces, il devient nécessaire de disposer d'antennes conformes, à hauteur réduite et multifonctionnelles. Dans les avions commerciaux performants, l'aluminium est graduellement remplacé par un matériau composite à base de fibres de carbone. Ce matériau a l'avantage d’offrir une résistance meilleure que celle de l'aluminium pour un poids équivalent et aussi de réduire les coûts d’enretien et de réparation. Dans cette thèse, quatre différents concepts d'antenne sont suggérés afin de réduire la hauteur d'une antenne, comparée aux antennes disponibles sur le marché pour des bandes de communications à Très Hautes Fréquences (VHF Comms 118-137 MHz), du système d'alerte de trafic et d'évitement de collision (TCAS 1.03-1.09 GHz) et du système d’équipement de mesure de distance (DME 0.96-1.22 GHz). Deux des concepts proposés sont basés sur le l’antenne en T avec des broches de court-circuit et des tronçons parasites pour rendre l’antenne à profil bas. Les deux autres concepts utilisent le chargement d’un monopole avec un matériau magnéto-diélectrique (MMD) et le chargement d’une antenne planaire avec un conducteur magnétique artificiel (CMA) pour rendre l’antenne à profil bas. Le premier design consiste en une antenne bi-bande couvrant à la fois les bandes Comms TCAS et VHF. Une antenne VHF d'un dixième à l'échelle physique a été étudiée précédemment dans notre groupe de recherche, se basant sur le concept de monopole en T avec broches de court-circuit et tronçons parasites.----------ABSTRACT In aircrafts, antennas are used for communications as well as for different navigation systems ranging from 30 MHz to 4 GHz and more. The placement of antenna on the aircraft is critical to avionic system of an aircraft. Typically blade antennas have been used in the aircraft for various communication systems. Blade antenna is basically monopole of height usually about a quarter of a wavelength to one-eighth of a wavelength and encapsulated in a radome. At low frequency the size of blade becomes large enough to introduce the acoustic noise and increase the parasitic drag of the antenna and do mechanical damage and collision with ground equipment during aircraft maintenance and service. Hence to improve the aerodynamics of efficient commercial aircrafts there is a need of reduced height, conformal and multifunction antennas. In efficient commercial aircrafts aluminum has been replaced by composite material, other than being expensive it has advantage of such as weight reduction, more strength than aluminum and has fewer maintenance and repair costs. In this dissertation four different antenna designs are proposed to reduce the height of an antenna as compared to commercially available antennas for Very High Frequency Communications (VHF Comms 118-137 MHz), Traffic Collision Avoidance System (TCAS 1.03-1.09 GHz) and Distance Measuring Equipment (DME 0.96-1.22 GHz) bands. Two of the designs proposed here are based on the concept of top-loaded antenna with shorting pins and parasitic stubs to make the antenna low-profile. The other two use the loading of a monopole with magneto-dielectric material (MDM) material and loading of a patch antenna with artificial magnetic conductor (AMC) to make the antenna low-profile. The first design is a dual-band antenna covering both TCAS and VHF Comms bands. Previously in our research group a physically scaled one-tenth of VHF antenna has been investigated, which uses the concept of top-loaded monopole with shorting pins and parasitic stubs. In this work the VHF antenna has been optimized and modified for full-scaled VHF frequency band. An interface plate has been added to the antenna structure so that it can easily be placed on any platform suitable for future testing or use. A novel approach has been used to feed the TCAS antenna placed over the VHF band antenna. Such design has an advantage of having dual-band coverage while using footprint of one antenna on the surface of an aircraft

Advancements in Automotive Antennas

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Imaging of buried utilities by ultra wideband sensory systems

Third-party damage to the buried infrastructure like natural gas pipelines, water distribution pipelines and fiber optic cables are estimated at $10 billion annually across the US. Also, the needed investment in upgrading our water and wastewater infrastructure over the next 20 years is estimated by Environmental Protection Agency (EPA) at$400 billion, however, non-destructive condition assessment technologies capable of providing quantifiable data regarding the structural integrity of our buried assets in a cost-effective manner are lacking. Both of these areas were recently identified several U.S. federal agencies as \u27critical national need\u27. In this research ultra wideband (UWB) time-domain radar technology was adopted in the development of sensory systems for the imaging of buried utilities, with focus on two key applications. The first was the development of a sensory system for damage avoidance of buried pipes and conduits during excavations. A sensory system which can be accommodated within common excavator buckets was designed, fabricated and subjected to laboratory and full-scale testing. The sensor is located at the cutting edge (teeth), detecting the presence of buried utilities ahead of the cutting teeth. That information can be used to alert the operator in real-time, thus avoiding damage to the buried utility. The second application focused on a sensory system that is capable of detecting structural defects within the wall of buried structures as well as voids in the soil-envelope encasing the structure. This ultra wideband sensory system is designed to be mounted on the robotic transporter that travels within the pipeline while collecting data around the entire circumference. The proposed approach was validated via 3-D numerical simulation as well as full-scale experimental testing

Design and development of multiband antennas for unmanned aerial vehicles (UAVs)

Abstract. This thesis aims to design and analyze microstrip patch antennas for unmanned aerial vehicles (UAVs) for Internet of Things (IoT) communication. With the growing need for reliable and efficient communication in UAV, understanding the unique challenges and requirements of antenna design for UAV-based communication systems becomes crucial. During the process of antenna integration onto the UAV body, important attention must be given to vital factors including the availability of mounting space, weight limitations, and radiation parameters. In this study, extensive efforts were made in the design of the antenna to meet the specific requirements for UAV applications. The antenna structure chosen was a microstrip patch antenna with an inset feed technique. The design aimed at optimizing the antenna for multi-band operation, ensuring compatibility with various communication frequencies. Careful considerations were made regarding size, weight, and functionality to ensure the antenna’s suitability for UAV applications. The first part of the thesis introduces the antenna theory, highlighting significant parameters such as radiation pattern, gain, and efficiency, which are crucial for UAV antenna design. The methodology for selecting various parameters is explained, and the radiation pattern and gain of two commercially available antennas were measured in the SATIMO chamber as a benchmark. The fabricated microstrip patch antenna was also tested both with and without the presence of a UAV to examine the impact of the UAV’s body on its performance. The designed antenna demonstrated a semi-omnidirectional pattern at sub-gigahertz frequencies, achieving a gain value exceeding 6 dBi, thereby fulfilling the requirements for UAV applications. The second part of this thesis focused on further advancements in the design process. Efforts were made to improve the antenna’s performance and behavior through various design modifications and optimizations. The design process involved iterative steps, such as adjusting the dimensions and parameters of the antenna to enhance its performance metrics. The results obtained demonstrated notable improvements in terms of radiation patterns with 92 degree of 3 dB angular beamwidth, gain enhancement up to 6.7 dBi, and overall antenna performance. These findings contribute to the body of knowledge in UAV antenna design and highlight the potential for further advancements in this field